Fuel Lock Issue

MitchT · 09-06-2018, 09:23 AM

On my '76 911: I finally got the 911 to turn over after a fuel lock issue. Cleaned spark plugs and cleaned and blew air through the injectors.
Tried to start it again and after turning it off it fuel locked again. I was able to manually turn it backwards and then forwards to release the pressure. When I disconnected the fuel relay and tried to start it, it started momentarily on the residual gas in the cylinders.
So I think something is pumping huge amounts of gas into the cylinders. I pushed the air valve upwards inside the air box and it doesn't have any resistance (with fuel pump on) like it should and it is not changing the flow of gas that I hear. The flow of gas I hear does not vary.
So is this a fuel distributor problem that is stuck in full flow position? Doesn't look like it is an easy part to get out of there with the air valve lever attached to it.
Any suggestions you have and solutions would really help.
Thanks again.

MitchT · 09-07-2018, 07:56 AM

Any one out there that can help on this issue?

boyt911sc · boyt911sc's Garage

Mitch,

Pull out all the six (6) injectors and place them in separate containers. Secure the containers and test run the FP. At this point, there should be no fuel delivery. If there is premature fuel delivery, take note which injectors are leaking. Keep us posted. Thanks.

Tony

T77911S · 09-07-2018, 08:46 AM

the plunger is probably stuck in the "up" position.
with the pump on and no resistance on the sensor plate is a tell tail sign.

remove the fuel distributor and pull the plunger out. probably all it needs is to be cleaned.
DO NOT drop it.

MitchT · 09-07-2018, 09:03 AM

Thanks to both and T77911S for focusing on the plunger issue. This is what I suspected. Do I need to separate the fuel distributor, top to bottom, to get the the plunger?

James Brown · James Brown's Garage

it might be bad injectors, we dont know yet till you do the "pull the injectors and place them in separate containers" check. plate closed=no fuel, plate full open=lots of fuel (fuel pump running) there might be one or two bad injectors stuck open, one step at a time
get the CIS primer book at M&K mufflers lots of good info

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by MitchT

Thanks to both and T77911S for focusing on the plunger issue. This is what I suspected. Do I need to separate the fuel distributor, top to bottom, to get the the plunger?

Mitch,

Before you even think of removing the FD, test and confirm what is causing for the fuel to be delivered prematurely. Do you have a CIS pressure gauge? Check your system pressure. If 70 psi. (system pressure) could not push or move the plunger down, I doubt you will able to get the plunger to move without disassembling the FD.

The fuel injector/s might be leaking(?). We don’t know that. Or worse, the FD is leaking. The test I suggested earlier is one of the tests I use to evaluate the condition of the injectors and FD. If the plunger is stuck above it rest position, this is a problem.

Tony

MitchT · 09-07-2018, 08:25 PM

Thanks Tony for the words of caution because I know opening up the FD should not be taken lightly. Not exactly understanding how the FD and injectors work together I'm wondering if the plunger is stuck in a full on position, wouldn't that effect the test of the injectors that has been suggested. Wouldn't they all just be full on and I couldn't determine if one or more is leaking?
I'm sure I'm missing something so an explanation from one who knows would help. It's such a strange problem.
Thanks again.

James Brown · James Brown's Garage

you will find out as soon as you turn on the fuel pump with the plate closed, have a friend turn on and quickly off if necessary, have a fire extinguisher standing by, a BIG one.

T77911S · 03:01 AM

you don't have to take the FD apart. just remove it and pull the plunger out and clean it.

with the FP on and no pressure on the sensor plate and fuel coming out of the injectors is a tell tail sign the plunger is stuck .
especially with enough fuel coming out to cause hydro lock.

Marc Bixen · Marc Bixen's Garage

You may have a blocked fuel return circuit. Check for rust in the tank. Remove the return line at the tank and see if fuel flows out. A blockage on the return will cause excessive fuel pressure and flood the cylinders. That'll be $20 please.

MitchT · 09-14-2018, 02:24 PM

Update: I pulled the fuel distributor and the piston was stuck in the up position. After applying carb cleaner I was able to grab hold of the bottom of the piston and pull it out. Cleaned it all up and re-installed it. Did a short bleed of the system and then the car started right up. Since there is not much on this site regarding fuel distributors I am posting two pictures to help others. As noted by others the tell tale sign of this problem is the air valve/lever in the air box had no resistance to it when I pushed it up and of course the resultant fuel lock that occurred. In the up position it was flooding the cylinders.
Thanks to all and to Kurt here in N. Arizona.
First picture is piston stuff in up position.
Second picture is piston free to move up and down.

James Brown · James Brown's Garage

all is well in the universe, good job

T77911S · 09-18-2018, 03:19 AM

Quote:

Originally Posted by Marc Bixen

You may have a blocked fuel return circuit. Check for rust in the tank. Remove the return line at the tank and see if fuel flows out. A blockage on the return will cause excessive fuel pressure and flood the cylinders. That'll be $20 please.

your check bounced.

a blocked return line would increase the control pressure putting more force on top of the piston pushing it down trying tying to shut the fuel off to the injectors.

it would also put more fuel pressure on the lower chambers in the fuel distributor again, trying to shut off fuel to the injectors.

to the OP, good job. glad to hear.